A gas turbine blade is exposed to a high temperature operation gas. Therefore, an Nickel-base super alloy which contains quite a few amount of Al and Ti is commonly used for a member for forming a gas turbine blade so as to enhance an anti-creeping characteristics which is caused under a high temperature condition. Also, for dealing with a super high temperature condition, it becomes more common that a directionally solidified coagulant and single crystal member are used so as to regulate a directivity of crystal growth in the single crystal member.
On the other hand, a method is used in which a cooling agent flows in a gas turbine blade (hereinafter called a turbine blade and a temperature which is loaded to the turbine blade is maintained in a lower temperature.
According to such a method, coolant paths which expand in a longitudinal direction (in a vertical direction) in the turbine blade are formed such that a plurality of coolant paths are formed in a plurality of channels in a width direction of the turbine blade, the coolant agent returns at a section where the neighboring channels communicate each other at an end of the turbine blade; thus, a channel or a plurality of channels are formed in a winding manner.
That is, as shown in an isometric view for showing a part of a gas turbine blade in FIG. 9, a plurality of coolant paths 53, 53, 53 which expand toward a blade tip section 52 in a longitudinal direction (vertical direction) are separated by separating walls 54a, 54b, and 54c inside a turbine blade main body 51. A coolant agent returns at an end of the blade where the neighboring channels 53, 53 communicate each other; thus, the coolant agent flows in a winding manner so as to make use of its cooling characteristics.
The turbine blade main body 51 having such a structure is formed by a casting operation while forming a hole 55 for detaching a plurality of cores in a blade tip section 52. The hole 55 is plugged to a tip plug 56 having a corresponding shape to the hole 55 by a tungsten inert-gas arc welding (hereinafter called a TIG welding).
However, when the tip plug 56 is welded to the hole 55 formed on the blade tip section 52 in a TIG welding operation, there are problems in that it is difficult for edge preparation for the welding operation because it is complicated, skill and experience are necessary for the welding operation, and the cost for welding operation increases easily.
Also, in addition, for restricting a solidification cracking and liquation cracking in a post-welded area on a base member for a blade, a method in which a lid is attached on the blade tip on a significant part of the blade and a plug is welded to the blade tip section by using a laser beam is used. Also, a method for a gas turbine blade in which a lid is welded to the blade tip section is used. These methods are not described with reference to drawings in the present specification. According to these methods, the welding operation is conducted throughout the entire plug; therefore, a condition in the finished surface depends on factors such as a roughness and color on a plug surface. Also, it is not possible to control a space between a plug and a bottom plate section (55a in FIG. 3); thus, there are problems in that a melting depth alters, and to a matter worse, a crack occurs on the welded section.